Double-grid piezo-electric modulation



March 10, 193 A. M L. NICOLSON 1,795,117

DOUBLE GRID PIEZO ELECTRIC MODULATION Filed Jan. 25. 1927 POWER POWER flMP.

INVENTOR ALEXANDER McLEAN NICOLSON Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE ALEXANDER MGLEAN NICOLSONQ OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGN- MENTS, TO FEDERAL TELEGRAPH COMPANY, A CORPORATION OF CALIFORNIA DOUBLE-GRID PIEZO-ELECTRIC MODULATION Application filed January 25, 1927. Serial No. 163,324.

I This invention relates to a method and apparatus for producing electrical oscillations'of relatively high frequency, such for example as those having a frequency sufliciently high for use in so-called carrier ourrentor radio signalling, modulated at other frequencies, in accordance with the signal it is desired to transmit, and more particularly to such apparatus utilizing piezo-electric crystal devices for the conversion of acoustic signals .into' corresponding electrical oscillations, and also for the excitation and stabilization andcontrol of the high frequency oscillations to be modulated. I

It is an object ofthis invention to provide a method and apparatus in which separate paths and circuits are provided including separate control electrodes, operating on a space current in a thermionic amplifier, for the purpose of impressing thereon the low frequency oscillations produced by excitation of a piezo-electric device and corre sponding to the speech, music or the like, which it is desired to transmit, and the high frequency oscillations which it is desired to modulate in accordance with the low frequency oscillations.

It is a further object of this invent1on to provide such apparatus which shall be selfexciting to produce the relatively high frequency oscillations desired, and which shall at the same time operate to stabilize and control the oscillations thereby produced, at the desired value.

Still other objects of this invention will be apparent from the specification.

Fig. 1 is a diagrammatic view of one form of apparatus according to my invention. Fig. 2 is a similar view of another form thereof.

In accordance with my invention, 1 provide a thermionic device comprising'a cathode and an anode, between which space current may flow, and provided with a plurality of control electrodes, such for example as grids. I preferably utilizeone of the control electrodes or grids for the purpose of controlling the space current in accordance with the high frequencyoscillations desired to be produced,- 'andthe other for the purpose of controlling the space current in accordance with the signals to be transmitted as modulations of the high frequency oscillations.

The oscillations corresponding to the signals desired to be transmitted, such as speech, music and the like, are generated in a piezoelectric crystal device provided with a pair of electrodes and arranged to be vibrated by the sound waves which it is desired to transmit as signals. For the purpose of preventing the passage of high frequency oscilla- 'tions through this piezo-electric crystal device, I may provide an impedance so adjusted as substantially to prevent the flow of high frequency currents therethrough, but offering little or no impedance to the passage of currents of audio frequency.

According to another, and in some instances preferred, embodiment of my invention, I may provide in the high freguency circuit, a piezo-electric crystal device having a natural frequency corresponding to the high frequency oscillations desired for transmission, and I may also arrange the thermionic device in such manner that energy from the output circuit is impressed upon the piezoelectric crystal device to maintain the same in vibration at the frequency desired for the high frequency signalling oscillations, whereby a self-excited system producing continuous oscillations of exactly the frequency desired, is obtained. I

The high frequency oscillations passing through the thermionic device are modulated by the low frequency oscillations. These modulated oscillations may be amplified to the extent desired and impressed upon a load circuit such as an antenna or a wire line.

Referring now more particularly to Fig. 1, 1 designates an oscillator of any suitable or preferred type, capable of generating electrical oscillations of the frequency desired by a suitable source of potential, such as battery 10. The anode 8 of the thermionic del I vice may be connected through a suitable coil 11 and a suitable source of potential 12, to the cathode circuit. 7

For the purpose of providing electrical oscillations corresponding to the signals, such as speech, music and the like, to be transmitted, liprovide'a piezo-electric crystal de vice 13 havingfapair of electrodes 14: and 15, and if desired, a pair of mounting plates 16 and 17. An acoustic device such as cone 18 may be secured to one of the mounting plates in such manner as to transmit to the crystal device vibrations impressed upon the cone -18 by the signals desired to be transmitted; a.

The electrode 14 is connected through suitable coil 19 to the grid or control electrode 7 of the thermionic device 5.

,The coil 11 may be inductively associated with a coil 20 forming theinput to a suitable power amplifier 21, the amplified oscillations from which may be passed through acoil 22 coupled to the coil 23, connected in antenna 24. Y 1

If now the various amplifiers be energized and the oscillator 1 set into vibration, the high frequency oscillations thereby produced will be passed through the coil 2 to coil 3,

andthereby impressed upon the input circuit "of the thermionic relay 5 comprising the control electrode '6' and the cathode 9. Space current flowing in said device will be controlled in accordance 'with the high frequency oscillations impressed upon the said input c1rcuit,1 and ifsound .waves are allowed to impinge upon the cone18, the crystal device 13 will be vibrated in accordance therewith,

and the electrical oscillations thereby produced will be impressed upon the control electrode 7, the effect of which. will be to I cause modulation of the high frequency oscillations appearing in the output circuit,'in

accordance with the; sound waves falling upon the cone 18. q The oscillator 1 may comprise any suitable source, such for example as a vacuumctube "oscillator having an arrangement for feeding back energy from-theoutput circuit to the 7 input circuit to generate sustained oscillations, and may comprise a piezo-electric crys- V tal device for controlling thefrequencythereof, as described in my copending application entitled "Generatmg and transmitting electrical currents, Serial No. 631,859, filed April 13, 1923.. The coil 19 and the condenser 4 will be preferably so adjusted as to prevent the flow of high frequency oscillations through the crystal'device 13, and conversely,

- to prevent the flow of low frequency oscillations through the high frequency circuit.

Referring now more particularly to Fig. 2, in case it is desired-toeliminate the separate oscillator 1, an arrangement may be provided for causing the thermionic relay. 5 to act as a generator of oscillations. For this purpose, there may be provided a piezo-electric crystal device 30, such as a quartz crystal, whose natural frequency corresponds to the high frequency at which it is desired to transmit. The crystal device 30 may be provided with suitable electrodes 31, 32, and 33: electrode 33 may be connected to the control electrode 6 of the thermionic relay 5, and electrode 31 to thefilament thereof. Electrode 32' may be connected to a suitable point on coil 11 whereby energy from the output circuit of the thermionic device may be impressed upon the crystal device to cause it to vibrate at its natural frequency, and thereby cause the production of an electromotive force between electrodes 31 and 33. In this instance, the sound waves impinging upon-the cone 18,

' cause the production of electrical oscillations shown the thermionic: device 5 as a single relay, it may, as a matter of fact, comprise any number of stages desired, only the first of which maybeprovided with separate control electrodes. I I r The piezo-electric crystal devices shown diagrammatically herein may be of any suitable material, size, shape and nature adapt ed to the functions to be performed, such as described in my copending applications, en-

titled Cast piezo-electric device, Serial No.

155,897, filed Dec. 20, 1926 Composite piezoelectric crystal device, Serial No. 155,898, filed Dec. 20,1926: Composite piezo-electric acoustic device, Serial No. 160,358,'filed Jan. 11, 1927 Internally clamped composite piezo-electric acoustic device, Serial No. 160,359, filed Jan. 11, 1927 and, Orientation .of component crystals in composite piezoelectric devices, Serial No. 155,902, filed Dec. 20,1926. g 1

While I have shown and described certain preferred embodiments of myinvention, it

will be understoodthat' modifications and changes may be made without departing from the spirit and; scope thereof, as willbe understood bythose skilled in the art.

I claim: I

A device for generating: modulated high frequency oscillations comprising, in oombination, an electron discharge device having an anode, a cathode, and two control electrodes, sources of energy for said electrodes, means for impressing high frequency oscillations between one of said control electrodes and said cathode, piezo electric means for controlling the frequency of said oscillations, an input circuit connected to the other control electrode and said cathode, a piezo electric device adapted to convert mechanical vibrations into electrical impulses and an inductance, said piezo electric device and inductance disposed in series in said input circuit, whereby said high frequency oscillations are modulated With said electrical impulses and reaction of said high frequency oscillations on said input circuit is prevented by said inductance.

Signed at New York city, in the county of 'New York and State of New York this 22d day of January A. D. 1927.

ALEXANDER MCLEAN NICOLSON. 

